The present invention relates to an image reconstruction method and an X-ray computed tomography (CT) system. More particularly, the present invention relates to a method of reconstructing an image on the basis of a plurality of views of projection data items provided by X-rays having passed through a subject, and an X-ray CT system performing the image reconstruction.
X-ray CT systems acquire a plurality of views of projection data items from a subject, and reconstruct an image on the basis of the projection data items. For the image reconstruction, processes such as pre-processing, reconstruction, and post-processing devised on the assumption of visual assessment of an image are employed. Therefore, even when computer-aided detection (CAD) is performed based on a reconstructed image, an image reconstructed on the assumption of the visual assessment is employed (refer to, for example, Patent Document 1).
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2004-070562 (pp. 4–5, FIG. 1)
In general, images for use in visual assessment have a high-frequency component thereof enhanced so that an image will appeal to naked eyes. Algorithms adapted to CAD include an algorithm that employs a differential filter. There is therefore a possibility that the differential filter function defined for CAD and a reconstruction function defined for visual assessment may enhance a noise to make recognition of an image, which is performed during CAD, unstable, and degrade a lesion image detection rate.